Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technique are widely deployed all over the world. High speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with highly competitive radio access technique in the mid-term future. However, since requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future. Decrease of cost per bit, increase in service availability, flexible use of frequency bands, simple architecture and open interface, low power consumption of a user equipment and the like are suggested as requirements of next generation communication systems.
Paging is an activity of a network calling one or more user equipments for a certain purpose. In addition to a basic function of enabling the network to search for a user equipment, paging also has a function of enabling the user equipment to be waken up from a sleep mode. The user equipment is in the sleep mode in normal times. The user equipment wakes up only when a paging channel is arrived from the network and performs an action requested by the network.
In the sleep mode, the user equipment should periodically wake up and confirm whether the paging channel is arrived. Waking up of the user equipment at periodic intervals, not at all times, is called discontinuous reception (hereinafter, referred to as DRX).
Unlike a base station, the user equipment operates using a battery. If the battery of the user equipment is not continuously recharged, the running time of the user equipment is limited. To increase the running time, the user equipment should be designed so as to minimize power consumption when the user equipment does not actually transmit or receive data.
There are various methods to save power consumption. A first method that conforms to the design criteria established due to the limited capacity of the battery of the user equipment is to minimize the time spent for the user equipment to confirm whether any data has been arrived at the user equipment. The time spent for the user equipment to monitor a channel that notifies arrival of data to the user equipment, such as a paging channel, is minimized. A second method is to transfer user data to the user equipment with a minimum delay time when there is the user data to be transferred from the network to the user equipment. The longer the time is taken from the point when the user data is created by the network to the point when the user data actually arrives at the user equipment, the more the quality of service felt by the user is degraded. The user data arrived at the network should be transferred to the user equipment as soon as possible in order to minimize the delay time. However, in order to reduce the delay time, the time spent for the user equipment to observe a paging channel t, such as a paging channel, should be increased.
Although the first and second methods described above are indispensable conditions for optimally operating the user equipment, they are conditions contradict to each other.
There is a need for a method for simultaneously satisfying both of the two conditions in the user equipment and the network.